The properties of ultra-thin films of metals of less than 10 nm thickness, are quite different to the properties of bulk metal. These metallic films may be transparent up to a thickness of 30 nm. The physical and chemical properties of these films are reviewed in the following references, which are believed to be representative of the state of the art: Kalyuzhny, G.; Vaskevich, A.; Matlis, S.; Rubinstein, I. Rev. Anal. Chem. 1999, 18, 237-242, and Kalyuzhny, G., Vaskevich A., Ashkenasy G., Shanzer A., and Rubinstein I. 2000, J. Phys. Chem. B 104, 8238-8244.
An article published on the Internet entitled Cranfield Biotechnology Centre-surface plasmon resonance appears at website www.cranfield.ac.uk/biotech/spr.htm describes use of reflected light for using surface plasmon resonance in diagnostic and sensing systems.
The following patents are believed to be representative of the state of the art: U.S. Pat. No. 5,449,918 to Krull et al., which describes a novel optical chemical sensor for direct and continuous detection of organic species in process streams employing thin metal island films, and U.S. Pat. No. 6,208,422 to Naya which describes a surface plasmon sensor including a dielectric block, a metal film having a sample supporting side which is faced toward a face of the dielectric block.